Over 10(11) metric tons of chitin are produced annually in the aquatic biosphere alone. Nevertheless, marine sediments contain only traces of chitin owing to the action of chitinivorous bacteria. The most ubiquitous marine bacteria are Vibrios, and we have shown that chitin utilization by V. furnissii is exceedingly complex. It involves the induction of several signal transducing systems, and many proteins including enzymes, transporters, an adhesion/deadhesion apparatus including a lectin, chemoreceptors, and probably specific porins and permeases. These studies bear directly on the problems of human health and disease. For example:(a)The chitin catabolic cascade has been linked to the virulence of human pathogens, including V cholerae, V parahaemolyticus, and V. furnisii. (b)Chitin is used for a variety of medical purposes, but there is little information on the catabolism of the oligosaccharides produced in vivo by lysozyme. (c)Other workers have shown that the hexosaminidase expressed by V. harveyi is similar to the alpha-chain of the enzyme defective in Tay-Sachs' disease. (d)The cascade is an excellent example of differential gene regulation. (e)The lectin is part of a nutrient sensing device in V. furnissii, and this may be true of other pathogens. Our long range goals are to determine the pathway by which chitin is utilized by V. furnissii, the mechanism underlying each of the steps, and how expression of this multitude of genes is controlled (they are differentially regulated). Six genes have been cloned from V. furnissii into E. coli, including one that encodes a chitinase(s). Some of the genes and gene products have been characterized, and similar studies will be conducted with the others. Special emphasis will be placed on cell associated and extracellular chitinases and their relationship to one another. We shall continue to search for other V. furnissii genes in the cascade using a variety of techniques including the chemical synthesis of gratuitous inducers for different steps in the pathway. Other methods will include biochemical characterization of gene products, and various molecular biological methods for determining the functions of genes and gene products. The proposed experiments will provide new insight into the turnover of a major component of the earth's biomass, and of problems of human health and disease.